Self-adjusting backflow preventor for centrifugal pumps

ABSTRACT

A PUMP IS DISCLOSED WHICH INCLUDES A CASING HAVING AN INLET, AN OUTLET AND A PUMPING CHAMBER DISPOSED THEREBETWEEN. AN IMPELLER IS ROTATABLY DISPOSED IN SAID PUMPING CHAMBER, AND SELF-ADJUSTING BACKFLOW PREVENTION MEANS IS DISPOSED ADJACENT SAID INLET FOR AUTOMATICALLY VARYING THE EFFECTIVE DIAMETER OF SAID INLET IN RESPONSE TO VARIATIONS IN BACKFLOW.

y 3, 1972 H. J. BIHELLER 3,664,759

SELF-ADJUSTING BACKFLOW PREVENTOR FOR CENTRIFUGAL PUMPS Filed Sept. 16,1970 HANS J BIHELLER INVENTOR.

UnitedStates Patent O 3,664,759 SELF-ADJUSTING BACKFLOW PREVENT OR FORCENTRIFUGAL PUMPS Hans J. Biheller, River-edge, N.J., assignor toWorthington Corporation, Harrison, NJ. Filed Sept. 16, 1970, Ser. No.72,650 Int. Cl. F04d 1/00, 15/00, 29/00 US. Cl. 415121 5 Claims ABSTRACTOF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates topumps, more particularly to pumps which exhibit backflowcharacteristics, and even more particularly to pumps which are providedwith selfadjusting backflow prevention means for automatically varyingthe effective diameter of the pump inlets in accordance with variationsin backflow.

As is well known in the art, centrifugal pumps exhibit thecharacteristic of partial backflow from the impeller eye into thesuction or inlet end of the pump when operating at flow rates below fullcapacity. This problem of partial backflow is especially severe forlarge high specific speed impellers and ordinarily results in reducedoutput as well as excessive noise and vibration.

In the past, the problems incident to partial backflow have beenalleviated by installing a reduced diameter throttle plate at or nearthe inlet end of the pump and as close as possible to the impller. Sucha throttle plate, in reducing the impeller eye inlet area, prevents orminimizes backflow into the suction line and its undesirable sideeffects. Although this prior art technique is satisfactory when the pumpis operating at low capacity, it presents distinct disadvantages whenthe pump is operating at higher capacities. Specifically, the reducedeye area of the impeller results in reduced pump output and also greatlyincreases the magnitude of pump suction pressure necessary to preventcavitation.

It is the principal object of the invention, therefore, to provide apump having backflow prevention means which prevent the backflow offluid into the pump suction line when the pump is operating at less thanfull capacity, which backflow prevention means reduces noise andvibration as compared to the noise and vibration ordinarily experienced,and which backflow means does not reduce the output capacity of thepump.

SUMMARY OF THE INVENTION The foregoing prinicpal object as well asothers not enumerated are accomplished by the pump of'the presentinvention, one embodiment of which may include a casing having inletopening means, outlet discharge means, and a pumping chamber disposedtherebetween; an impeller rotatably disposed in said pumping chamber;and selfadjusting backflow prevention means disposed adjacent said inletopening means for automatically varying the effective diameter of saidinlet opening means in response to variations in backflow.

In accordance with a preferred embodiment of the invention, theself-adjusting backflow prevention means comprises a plurality offlexible, wedge shaped members circumferentially disposed about theinlet opening to the pump. Each of the flexible members has one endthereof fixed with respect to the pump casing and another end thereoffreely disposed with respect to the flow of fluid through the inletopening of the pump. In this manner, the flexible members are flexed outof the flow path of fluid toward the impeller in response to increasingflow of the fluid toward the impeller. Similarly, the flexible membersare free to flex into suction flow restricting position in response toan increase in backflow, thereby effectively reducing the diameter ofthe suction line or input to the pump up on the occurrence of reducedpump loads.

As a particularly advantageous feature of the instant invention, thereis provided a fluid traversing backup means positioned in the pumpsuction line on the upstream side of the flexible members in theupstream direction. In one embodiment, the backup means may comprise ascreen whereby at normal flow conditions, i.e. with no backflow from theimpeller, the flexible members are flexed away from the screen and outof flow restricting position; whereas at reduced flow conditions, theflexible means are displaced partially or totally into contact with thebackup screen and thus into flow restricting position. The fluidtraversing backup means and the flexible members thus cooperate todefine a variable diameter annular flow restricting means, the diameterbeing variable in response to the occurrence of backflow from the pumpimpeller to preclude introduction of backflow into the suction line.

BRIEF DESCRIPTION OF DRAWINGS A more complete understanding of thepresent invention may be had from the following detailed descriptionthereof, particularly when read in the light of the accompanyingdrawings, wherein:

FIG. 1 is a cross sectional view of the fluid end of a pump constructedin accordance with the instant invention; and

FIG. 2 is an enlarged planar view of the self-adjusting backflowprevention means of the instant invention.

DETAILED DESCRIPTION Referring to FIG. 1, a pump structured according tothe invention is designated generally by the reference numeral 10.

Pump 10 includes a casing 12 having an inlet opening 14 and an outletopening (not shown) which is secured to a discharge line 16. Secured bysuitable bolts to a flange 17 formed on the inlet end of casing 12 is asuction line 18 having a flange 19. Rigidly secured between flanges 17and 19 such as to extend across the flow path of fluid from suction line18 to inlet opening 14 is a backflow prevention device according to theinvention, which device is designated generally by reference numeral 20and discussed below in detail.

The interior of casing 12 defines a pumping chamber 21 within which isoperably positioned an impeller 22. Impeller 22 is rigidly mounted on ashaft 24, which shaft is received for rotation within bearing 26 anddriven by a suitable means such as an electric motor (not shown). Thus,the operation of the driving means imparts rotation through shaft 24 toimpeller 22 thereby establishing a flow of fluid from suction line 18,through inlet opening 14, centrifugally through the impeller blades intoa conventional volute 25 and thereafter out of the pump dischargeopening into discharge line 16. The amount of fluid passing throughdischarge line 16 is often regulated externally from the pump bysuitable valve means. Thus, if the flow of fluid through discharge line16 is restricted such as to reduce the flow below the capacity of pump10, the situation of back flow described above occurs. Morespecifically, although the impeller 22 of pump 10 is being driven at aspeed suflicient to pump fluid at full capacity through the pump, suchfull capacity flow is not permitted by the restriction in discharge line16.

As is recognized in the art, the restriction of discharge flow fromcentrifugal pumps such as pump 10 causes a significant backflow from theimpeller eye toward suction line 18. The backflow of fluid is an annularflow around the flow of inlet fluid from suction line 18 and adjacentthe inner surface 28 of inlet opening 14. In the absence of some type ofbackflow prevention means, the backflow would continue into suction line18. As is discussed above, such backflow into the suction line isundesirable and thus the prior art has resorted to the use of backflowpreventing devices such as throttle plates disposed adjacent the inletof a pump for the purpose of eliminating backflow into the suction line.

The ordinary throttle plates known in the prior art are manufactured toaccommodate a particular design flow condition, which flow condition isless than the full flow capacity of the pump. Their use has provenunsatisfactory, however, when the flow through the pump is at a rateother than that for which the throttle plate was designed. Specifically,the flow restricting throttle plate reduces the total capacity of thepump in addition to being a potential source of vibration, cavitationand other problems.

The present invention avoids the problems experienced in the prior artby providing a pump having a variable diameter inlet orifice, thediameter of which varies in response to variations in backflow, theamount of which backflow is a function of the amount of fluid beingpumped as compared with the full flow capacity of the pump. The variablediameter inlet orifice is embodied in backflow prevention device 20which, as noted above, is secured between the flanges 17 and 19 of pumpinlet 14 and suction line 18, respectively.

Referring therefore to both FIGS. 1 and 2, the depicted embodiment ofbackflow prevention device 20 can be seen to comprise a plurality offlexible, generally wedge shaped members 32 which are secured on agenerally circular coarse screen 36 by suitable means such as rivets 38.Wedge shaped members 32 are disposed on screen 36 such as to define agenerally annular [flow restricting ring having an outside radius R andan inside radius R,.

Wedge shaped members 32 may be manufactured from any of many flexiblematerials such as rubber, leather, plastic and the like, limitations asto the selection of the materials being only that they be sufficientlyflexible to accommodate deflection as required during operation and thatthey be compatible with the fluid being pumped.

As noted above, the backflow from the eye of a centrifugal pump duringoperation at less than capacity is an annular flow away from theimpeller toward the suction line. As the fluid being discharged from thepump through discharge line 16 approaches the full capacity of the pump,the volume of backflow fluid decreases. Thus, the operation of backflowprevention device 20 is best explained in terms of operation at fullflow conditions, minimum flow conditions, and intermediate flowconditions.

Considering initially the characteristics of backflow prevention device20 during minimum flow conditions, i.e. during conditions of minimumbackflow, the physical orientation of segments 32 is shown for theseconditions in broken line in FIG. 1 and in solid line in FIG. 2.Specifically, during periods of minimum flow from discharge line 16,wedge shaped segments 3-2 extend radially inwardly adjacent screen 36and cooperate to define a circular inlet opening having a radius R Withthe wedge shaped segments so disposed, backflowing fluid flows adjacentthe surface of inlet opening '14 toward backflow prevention device 20until, adjacent the surface of segments 32, the baokflowing fluid iscaused to flow inwardly and join a fluid from suction line 18, thecombined fluids thereafter being drawn toward impeller 22.

Upon the occurrence of an increased flow of discharge fluid through line16, less fluid is caused to backflow and more fluid is drawn fromsuction line 18. Thus, wedge shaped segments 32 are displaced from thepositions shown in broken line in FIG. 1 to the positions shown in solidline in FIG. 1, i.e. from a minimum fluid flow condition to anintermediate fluid flow condition. As is evident from FIG. 1, thedisplacement of wedge shaped segments 32 toward the surface of inletopening 14 eflectively increases the size of the opening through whichfluid is drawn from suction line 18. Thus, with the wedge shapedsegments disposed as shown, the increased requirement for fluid fromsuction line 18 is accommodated through the increased opening defined bythe inner edges of segments 32 without adversely effecting thecapability of wedges 32 from preventing the backflow of fluid intosuction line 18.

Upon the occurrence of a further increase in the amount of fluid beingdischarged through discharge line 16 to the point of maximum pumpcapacity, virtually no backflow is experienced and segments 32 areflexed fully outwardly toward the surface of inlet opening '14 so as topermit the flow of fluid from suction line 18 to proceed virtuallyunrestrictedly into the suction eye of the impeller 22. In this regard,segments 32 are displaced to be adjacent the surface of inlet opening 14as shown in phantom line in FIG. 1 and thus the only restriction of theflowing fluid that occurs during maximum flow conditions is theresistance presented by coarse screen 36. The screen being coarse,however, it does not present resistance which is of significance andthus as a source of flow restriction can be disregarded.

Upon a decrease in fluid flow through pump 10 from maximum, theresiliency of the segments 32 coupled with the force exerted thereon bythe occurrence of laminar backflow as discussed above, cause thesegments 32 to be displaced away from the surface of inlet opening 14thereby decreasing the size of the opening communicating suction line 18with inlet opening 14 as well as preventing the backflow of fluid fromadjacent the surface of inlet opening 14 into suction line 18. Thesegments 32 continue to deflect radially inwardly as the flow of fluidthrough discharge line 16 is decreased until the point of minimum flowis achieved, at which point the segments 32 are disposed as shown inbroken line in FIG. 1. Thus, it will be appreciated that the pump 10incorporating backflow prevention device 20 embodies a pump havingthereon a backflow prevention device which automatically varies theeffective diameter of the pump inlet in response to variations in thebackflow of fluid. If designed properly, backflow prevention device 20will suitably accommodate the entire range of flow rates of which thepump is capable.

It is to be recognized that although backflow prevention device 20 isshown as being disposed between the flanges 17 and 19 of pump 10 andsuction pipe 18 respectively, the device could also be mounted withininlet opening 14, eg by providing an annular channel 42 (shown in brokenline in FIG. 1) in the surface of inlet opening 14 and mounting thebackflow prevention device by suitable means such as a spring ring orthe like.

The foregoing detailed description relates to a preferred embodiment ofthe invention. It is to be recognized, however, that many modificationsand variations to the invention can be accomplished without departingfrom the spirit and scope thereof.

What is claimed is:

1. In a centrifugal pump,

a casing forming a pumping chamber having a centrally disposed inletopening and a discharge outlet,

an impeller rotatably disposed in said pumping chamher and having asuction eye communicating with the inlet opening,

backflow preventor means connected to the casing transversely of thecenter line of the inlet opening and disposed for operative coactionwith said impeller to automatically vary the effective diameter of theinlet opening in response to variation in backflow in said pumpingchamber,

said means comprising a ring of flexible members each having one endthereof fixedly connected to the casing and the end opposite from thefixed end freely movable from a predetermined minimum position to apredetermined maximum position with variations in backflow,

and back-up means coacting with each of said flexible members tomaintain said predetermined minimum inlet opening at maximum baokflowconditions in said pumping chamber.

2. In a centrifugal pump as claimed in claim 1 wherein the inlet openingis of circular cross-section and the means to prevent backflow includesa plurality of flexible members connected circumferentially about saidinlet opening in substantially the same transverse plain, said flexiblemembers sized so that the planar area of said flexible members is lessthan the cross-sectional area of said inlet opening at the predeterminedminimum inlet opening position of said flexible members.

3. In a centrifugal pump as claimed in claim 1 wherein the back-up meansis disposed on the upstream side of the flexible members to preventflexing of said flexible members in a direction opposite to thedirection of fluid flow to said impeller.

4. In a centrifugal pump as claimed in claim 2 wherein each flexiblemember is generally wedged shaped in plan view and each wedged shapedflexible member at the outer end has a radius approximating the radiusof said inlet opening and at the inner end a preselected radius todefine a minimum inlet opening, said flexible members eifectivelydefining at predetermined minimum flow conditions a cross-sectional arealess than the cross-sectional area of said inlet opening.

5. In a centrifugal pump as claimed in claim 1 wherein said back-upmeans comprises a screen member.

References Cited UNITED STATES PATENTS 3,483,824 12/ 1969 Sprague 4151473,362,624 1/1968 Endress 415147 3,289,919 12/1966 Wood 415150 2,692,08010/ 1954 Schwaiger 415147 3,174,434 3/ 1965 Schieve 415146 3,586,0406/1971 Urback 41511 890,117 6/1908 Austin 415147 1,353,915 9/1920 Kime41526 2,332,875 10/1943 Stratton 415147 2,908,283 10/1959 Kiifer et a1.137-525.3 2138.5,730 9/1945 Read 415147 3,463,189 8/1969 Fritzpatrick137----525.3

FOREIGN PATENTS 1,092,221 11/1960 Germany l37525.3 559,321 3/1957 Italy137525.3

HENRY R. RADUAZO, Primary Examiner US. Cl. X.R.

